1. Field
The present disclosure is directed to a method and apparatus for operating a switchmode power supply. More particularly, the present disclosure is directed to operating a switchmode power supply at a higher frequency than a pulse width modulation controller pulse width modulation frequency.
2. Introduction
Presently, a switchmode power supply is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. The switchmode power supply transfers power from a source to a load, such as a portable electronic device, while converting voltage and current characteristics. A pass transistor of a switchmode supply continually switches between low-dissipation, full-on, and full-off states, and spends very little time in the high dissipation transitions, which minimizes wasted energy. Voltage regulation is achieved by varying the ratio of on-to-off time.
Switchmode power supplies that are designed around digital controllers are limited in operational frequency by the maximum computational speed of the digital controller that supplies the switching signal. For example, adequate pulse width modulation duty cycle control, such as with 6 bits or more, requires dividing down the controller clock, so a 16 MHz controller can only operate a 400 kHz switchmode supply at 6 bits, where 400 kHz=16 MHz/2^6. Also, digital switchmode power controllers are limited in their output voltage swing and cannot drive typical power semiconductor devices without buffers and level shifting, which cost space, money, and power.
Thus, there is a need for an improved method and apparatus for operating a digitally controlled switchmode power supply.